There has been over 130 years of research into the treatment of breast cancer using approaches that target oestrogen receptor signalling. Here, we summarise the development of the key pillars of such endocrine therapy, namely, oestrogen deprivation, achieved through ovarian suppression and/or aromatase inhibition, and oestrogen receptor blockade, through selective oestrogen receptor modulators, downregulators and novel compounds entering early phase development. The translation of these compounds from advanced to early breast cancer settings is discussed with a focus on the placebo-controlled breast cancer prevention studies to most accurately describe the side effect profiles of the main approaches.